1. Field of the Invention
The present invention is in the field of glass manufacture, being directed specifically to a method for forming a cut or cuts in a band of hot glass emerging from the terminal end of a manufacturing process, such as a float line.
2. The Prior Art
In my copending application Ser. No. 426,526, reference is made to a process for the direct manufacture of tempered glass sheets. The method of that application involves subjecting a continuously advancing glass band to a substantial quench of at least one of its surfaces, effecting a conventional scribing in the quenched area, breaking the glass along the scribe line by a rapid flexure, and continuing the quench process until tempering has been completed.
As is known, when glass at tempering temperatures, e.g. in the order of about 1250.degree.F for a conventional soda-lime composition, is subjected to quenching influences, the surface areas are initially placed in substantial tension. Further in the quenching cycle, the tension in the surface areas is progressively reduced, and with the cooling and consequent shrinkage of the interior elements of the glass, the surfaces are placed under substantial compression.
The method of application Ser. No. 426,526 is predicated upon the discovery that during a quenching procedure incident to tempering, and particularly at that phase or range of the tempering procedure wherein the tension of the surface of the glass is reduced and the surface is about to enter or has just entered the compressive phase, the surface of the glass may be scribed and broken, and the resultant sheet obtained by continuing the quenching procedure will not evidence any of the tendencies to dice which would be experienced from an attempt to scribe and break a tempered glass sheet.
The method in accordance with application Ser. No. 426,526, in short, is directed broadly to the concept of cutting during the quench cycle, and in the discovery broadly that a glass sheet within the temperature range suitable for tempering may be broken by cooling a surface, scribing the cooled surface and breaking along the scribe while a substantial temperature differential exists within the sheet.
As hereinabove noted, the scoring and breaking in accordance with the described embodiments in application Ser. No. 426,526 are concluded to have been effected in the quenching process at that point or in that range when the cooled surface has already progressed through its major tension condition and is about to enter or has just entered a compression state or is at a null condition.
Without being bound by any theory, it is believed that the success of the procedure in the aforesaid application was predicated upon the fact that by cutting at the stage noted, the fissures in the surface resulting from scoring were not present at any time when the surface was in a state of high tension. Although such fissures may remain after cutting and breaking, they do not spread since they exist only in compression zones of the glass.
In contrast, conventional tempering of annealed glass requires that the edges of the sheet be ground to remove fissures which would spread when the surfaces are placed in tension in the course of quenching.
There may be mentioned, in addition to the prior art patents cited in the text of application Ser. No. 426,526, U.S. Pat. No. 3,754,884, This patent suggests that tempering may be effected, with the saving of some of the heat of melt, by reducing the temperature of a band of glass emerging from a melt to a uniform value below the temperature at which the glass is self-sustaining, such temperature being about the strain point of the glass, and cutting the glass at such uniform elevated temperature.